Time evolution of an infinite projected entangled pair state: Neighborhood tensor update

The simple update (SU) and full (FU) are the two paradigmatic time evolution algorithms for a tensor network known as infinite projected entangled pair state (iPEPS). They differ by an error measure that is either, respectively, local or takes into account environment. In this paper we test intermediate neighborhood (NTU) accounting nearest neighbor This small environment can be contracted exactly in parallelizable way. It provides Hermitian non-negative down to machine precision. 2D quantum Ising model NTU shown yield stable unitary following sudden quench. also yields accurate thermal states despite correlation lengths reach up 20 lattice sites. latter simulations were performed with manifestly purification of state. Both reduced tensors do not include physical (and ancilla) indices. modification naturally leads other schemes: SVD (SVDU) (FTU) being variant FU.